from random import choice

def complementRNA(base):
  if base == 'A':
    return 'U'
  elif base == 'U':
    return 'A'
  elif base == 'C':
    return 'G'
  elif base == 'G':
    return 'C'
  else:
    return '?'

def genRNA(len):
  code = ""
  for i in range(len):
    code += choice("AUGC")
  return code